Radial flow reactors are widely used to contact fluid reactants that are typically gaseous with particulate catalyst. Radial flow reactors typically include a cylindrical vessel with an inlet at one end and an annular chamber or series of chambers arranged annularly around the interior periphery of the vessel for distributing reactants to an annular catalyst bed disposed inwardly of the reactant distribution chamber(s). A centerpipe is disposed inwardly of the annular catalyst bed and is in communication with a reactor outlet for the exit of product from the reactor. The annular distribution chamber(s) and the centerpipe are permeable to fluid flow but impermeable to catalyst flow to contain the catalyst bed therebetween.
Examples of processes carried out in such an apparatus include various hydroprocessing techniques such as catalytic reforming, catalyst regeneration, hydrotreating, dehydrogenation of butane, dehydrocyclodimerization and isomerization. Various catalysts and processes have been developed to effect xylene isomerization. In selecting appropriate technology, it is desirable to run the isomerization process as close to equilibrium as practical in order to maximize the yield of the desired xylene isomer, which is usually para-xylene, but can be meta-xylene or ortho-xylene.
In the isomerization of mixed xylenes to para-xylene, the most difficult component to deal with is ethylbenzene. Ethylbenzene is not easily isomerized to xylenes. Moreover, separation of ethylbenzene from xylenes in the effluent from the isomerization reactor by superfractionation or adsorption is very expensive. A widely used approach is to isomerize xylenes to obtain an equilibrium amount of desirable xylene isomer and to dealkylate ethylbenzene to form principally benzene over an ethylbenzene dealkylation type xylene isomerization catalyst. This approach commonly results in higher ethylbenzene conversion and more effective xylene isomerization, thus lowering the quantity of recycle in a loop of isomerization/para-xylene recovery and reducing concomitant processing costs. An alternative approach is to react the ethylbenzene to form a xylene mixture via conversion to and reconversion from naphthenes in the presence of a solid acid catalyst with a hydrogenation-dehydrogenation function. This approach enhances xylene yield by forming xylenes from ethylbenzene. A process that achieves conversion of ethylbenzene to xylenes, xylene isomerization and dealkylation of unconverted ethylbenzene to benzene utilizes both approaches with a two-catalyst system. Such a two-catalyst system is disclosed in U.S. Pat. No. 6,222,086 B1, which is incorporated herein by reference.
WO 99/20384 discloses a radial flow reactor with two annular catalyst beds disposed between an annular reactant distribution chamber and the centerpipe of the reactor. Catalyst loading into this reactor requires use of a cylindrical form which is placed into the radial flow reactor while respective catalyst beds are loaded inside and outside of the cylindrical form to provide two annular catalyst beds. The cylindrical form is then removed after loading of the catalyst.
Loading two separate catalyst beds using a cylindrical form can be labor-intensive. Matters are complicated when one or both of the catalyst beds must be loaded in an inert environment perhaps because they are sensitive to degradation by oxidation. In such a case, catalyst loading labor must be specially trained and must utilize special equipment. Moreover, when loading the two catalyst beds between the centerpipe and the annular distribution chamber(s), both catalysts must share the volume of the annular catalyst bed, thereby diminishing the volume of each of the catalysts that may be loaded into the radial flow reactor.
An object of the present invention is to provide an improved radial flow reactor that contains two annular catalyst beds.
Another object of the present invention is to provide a method of loading the two catalyst beds of the improved radial flow reactor and a process of using the improved radial flow reactor.